A long-term posttraumatic study in the rat median nerve crush injury model

The possibility that posttraumatic regeneration may eventually lead rat peripheral nerve fibers back to normal is still under debate. While it has been shown that, after a sufficiently long posttraumatic time, the number of regenerated rat peripheral nerve fibers can return to normal levels and the animal can regain normal pre-lesion function, no information regarding long-term changes in size parameters of regenerated nerve fibers is still available. To fill this gap, 24-week posttraumatic changes in myelinated axon and nerve fiber diameter, myelin thickness and g-ratio (axon diameter/fiber diameter), distal to a nerve crush (axonotmesis lesion) of the rat median nerve were assessed by stereology. Results showed that, while as expected fiber number returned to normal values at week-24, both axon and fiber diameter and myelin thickness were still significantly lower at week-24 in comparison to pre-lesion values. Finally, g-ratio, which persisted unmodified along the regeneration process, eventually resulted to be significantly reduced at week-24 in comparison to pre-lesion value. Based on these results, the hypothesis that regenerated rat peripheral nerve fibers are able to spontaneously return to normal, provided that a sufficiently long time recovery post-axonotmesis is allowed, is rejected